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SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond. Lecture 8 24 February 2014 Science Center Lecture Hall A. Today ’ s Tantalizing Tales (Outline For Lecture 8). Composition of universe (dark mysteries):
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SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond Lecture 8 24February 2014 Science Center Lecture Hall A
Today’s Tantalizing Tales(Outline For Lecture 8) Composition of universe (dark mysteries): - Dark matter: First glimmer to present status - Dark energy: Standard candles to startling results Overall results on composition (including us) Age of universe Concept of multiverses
Dark matter: Initial Inklings Estimate of mass of bound systems of galaxies: - How know that galaxies are gravitationally bound? - Is inferred mass consistent with what is needed to bind? How know what is needed? - Who noticed such a problem and when? Fritz Zwicky in 1931 (see next three slides)
What Did Zwicky Conclude? His observations showed that galaxies in cluster were moving too fast to be bound together gravitationally. Since very unlikely that he observed just as galaxies were flying apart, they must be bound. Since not enough visible mass (inferred from brightness), mass responsible for binding must not be visible: It must bedark
What Happened Next? Zwicky’s results were largely ignored, despite no one’s finding flaws in his data or his logic. This mystery lay fallow for about 4 decades. Then it came front and center because of new discovery, consistent with it. New discovery, made possible by improvements in technology, described in next few slides
Galaxy Rotation Curves 1970s observations of Vera Rubin and Ken Ford of “flat” rotation curves (see next few slides) caused a stir, especially after later confirmatory evidence gathered by others Why was there concern about the lack of “fall off” in these curves?
Schematic of a Galactic Rotation Curve: A was expected; B was observed
Clues To Speed “Fall Off” Mass of galaxy concentrated towards center Kepler’s third law shows (circular) orbital speed falls with distance as 1/√a, i.e., as inverse square root of distance from central mass (see Homework Assignment No. 1)
Scientists Were Convinced: Dark Matter Exists! Why “dark”? What is it? How can one find out? How is it distributed in space? How does it interact with“ordinary” matter and light? Address questions through particle-physics speculations, laboratory experiments, and numerical modeling of evolution of galaxies and universe Recent: LUX (=Large Underground Xenon) experiment: Shows no evidence for “WIMPs” (=Weakly Interacting Massive Particles)
Bottom Line No one knows what Dark Matter is. We grope in the dark!
Future Of Universe: What Is Its Fate? Will it expand forever or will it eventually collapse? (Key demo) How can we find out? Standard candles, supernovae Ia, to fore: Measure rate of expansion, called Hubble constant, H (H0 is current value) vs. past time (distance from us)
Measuring Change In Rate Of Expansion Of Universe If H larger in past, universe is decelerating (rate of expansion is decreasing as time progresses) If H sufficiently larger in past, universe’s expansion will (eventually) stop and start to collapse towards the “Big Crunch” How to distinguish? Measure
Race For “Gold Cup” Of Astronomy Two main groups competed to measure change in H vs. time: one centered on West Coast (University of California Berkeley) and one centered on East Coast (Harvard) Required measurements had many pitfalls and subtleties (e.g., corrections for light-absorption by dust between supernovae and us) What were possible outcomes?
Startling End Of Race Substantial “he said; she said” claims and counterclaims; all true and verifiable, but how to relatively weight to properly decide on winners? (You may say: Why bother? Egos – and prizes – involved.) Main point by far: Dramatic, totally unexpected and unpredicted result -- Universe is not decelerating but accelerating!(See next slide.) How could this be?
Anti-Gravity Exists! Dubbed “Dark Energy” Why “dark”? Why “energy”? What model do we have, consistent with these observations? Particle physics offers result about factor of 10120too large! “Fudge factor” that Einstein introduced to allow universe to be static – “The Cosmological Constant” - has arisen from dust-bin of history as model of anti-gravity consistent with observations of supernovae, to within uncertainty of about 5% So why don’t we fly off earth in response to anti-gravity?
Dark Energy: All Over But The Shouting? Plenty of shouting: Discovery of decade (at least); Nobel Prize in physics for 2011 (two East Coast and one West Coast winner; see next slide) As yet no fundamental theory that “explains” dark energy. Development of model that also encompasses dark matter is major challenge of early 21st century in both astronomy and physics Any respectable doubters? Yes, but fewer and fewer [e.g., MOND (=MOdified Newtonian Dynamics) believers]
So What Is The Universe Made Of Overall? ~ 70% dark energy ~ 25% dark matter ~ 5% “ordinary”matter; matter that we know and love is almost insignificant part of whole; of course, it does include us, which thus changes our perspective a bit
Age Of Universe According to Planck: 13.8 Billion years According to WMAP: 13.7 Billion years Conclusion: Universe’s age accelerating - 100 million years in under 5 years! (Joking, of course.) Note: CMB “kicks in” at c. 380,000 years
Cosmology: Contemporary Beliefs In Brief Big Bang Inflation ------------------- Cosmic Microwave Background Structure (galaxies, stars, planets, dust, and gas) Dark Energy + Dark Matter + “Ordinary” Matter and Radiation
Proposed Final Stage Of Our Demotion Previously noted: earth minor planet orbiting ordinary star, far from center of run-of-mill galaxy, one of about 100 billion (not that anyone has done exact census). How much further can we sink? You will be amazed: Multiverse hypothesis. Idea goes back to Hugh Everett III in late 1950s. Fundamental constants tuned for life. Really we’re one out of ~10500 “parallel” universes! Now into realm of religion: can’t falsify
